48 BACTERIOLOGY. 



action of disinfectants; and the process is, therefore, 

 known as disinfection, though the same end can also 

 be reached by the application of heat to these articles. 

 Strictly speaking, sterilization implies the complete de- 

 struction of the vitality of all micro-organisms that 

 may be present in or upon the substance to be steril- 

 ized, and can be accomplished by the proper application 

 of both thermal and chemical agents ; while disinfec- 

 tion, though it may, need not, of necessity, insure the 

 destruction of all living forms that are present, but only 

 of those possessing the power of infecting; it may or may 

 not, therefore, be complete in the sense of sterilization. 

 From this we see it is possible to accomplish both steril- 

 ization and disinfection as well by chemical as by ther- 

 mal means. 



In practice the employment of these means is gov- 

 erned by circumstances. In the laboratory it is essen- 

 tial that all culture media with which the work is to be 

 conducted should be free from living bacteria or their 

 spores they must be sterile and it is equally impor- 

 tant that their original chemical composition should re- 

 main unchanged. It is evident, therefore, that steriliza- 

 tion of these substances by means of chemicals is out of 

 the question, for, while the media could be thus steril- 

 ized, it would be necessary, in order to accomplish this, 

 to add to them substances capable not only of destroying 

 all micro-organisms present, but whose presence would 

 at the same time prevent the growth of bacteria that are to 

 be subsequently cultivated in these media that is to say, 

 after performing their sterilizing or germicidal function, 

 the chemical disinfectants would, by their further pres- 

 ence, exhibit their antiseptic properties and thus render 

 the material useless as a culture medium. Exceptions 



